Recharts sizes every tick and label by writing it into one off-screen
span and reading getBoundingClientRect(). Under <body> each read forced
a document-wide style recalc, because the stylesheet's descendant-subject
:has() rules leave Chromium no way to scope the invalidation. A seeded
dashboard made 149 such reads per cold load at about 2.8 ms each, about
1.8 s of main-thread time under a 4x CPU slowdown.
The chart runtime now parks that span in a zero-size, contain: strict
host under <html>, which Recharts finds by id and keeps using. Each read
drops to about 0.01 ms; the dashboard's total blocking time under the
same slowdown falls from about 2.5 s to about 0.75 s. The host copies
<body>'s classes, where the app font is set, so every string measures
exactly as before; an e2e spec checks that parity on the drawn labels
and that the host survives a client-side round trip.
